This invention relates to an improved web guiding system incorporating a feeler-type edge sensor utilizing fiber optic cables to transmit signals to allow the detection of a web position without distorting the web edge.
Feeler-type edge sensors have been used for many years in the processing of textile webs. The feeler-type sensor typically has a depending feeler finger which engages the web edge. This is good for positively and accurately sensing the position of the edge, particularly for woven fabric often having untucked selvages. However, the feeler-type sensors have required heavy mechanical input on the feeler to effect changing the electrical contacts. Additionally, these have required heavy springs or counter weights to prevent the feeler from "bouncing" during high speed movement. The heavy force required to counter these weights and springs usually distorts the web edges, making these sensors impractical for most applications. Examples of feeler-type sensors are shown in U.S. Pat. Nos. 2,448,639, 3,569,642, and 3,873,789.
As a result of the web distortion and bouncing problems associated with the use of feeler-type sensors, the industry has selected direct photo electric, beam breaking, or air jet resistance type sensors. These sensors do not physically contact the web edge, but rather attempt to accurately detect the edge location by interruption of an energy beam, i.e. light, air, etc. However, these noncontact senors have the disadvantage of easily becoming impaired in web edge detection. For example, photocell type light sensor become quited easily reduced in reliability with variations in the translucency of the web, and require frequent adjustment to web translucency. In the case of woven webs, there is often an untucked selvage. This means that loose yarns or threads may extend randomly from the edge. These untucked strands may easily falsely trigger the photocell as the edge of the web. Further, the sensors are subject to lint conditions which, in the case of a photocell, can cover the eye and impair dependability. When used to sense web edge location on coating machines, the photocell eye can easily become blocked by coating material falling on the eye.
Typical applications of web edge sensors are to guide textile webs on tenters and on coating machines. These applications often require that water be used for clean up. The prior contact and non-contact type web edge sensors are highly susceptible to water and moisture damage when used in this type environment.
Accordingly, an object of the invention is to provide a web edge sensor for guiding a web which accurately senses a web edge using light physical contact with the web and which also incorporates the positive switching aspects of energy beam interruption.
Another object of the invention is to provide a web edge sensor having a feather light feeler action for sensing the edge of a web without distorting the edge.
Another object of the invention is to provide a feeler-type web edge sensor in which bouncing is reduced during high speed web movement past the feeler.
Another object of the invention is to provide a web edge sensor having a feather light action which senses a web edge with reduced bouncing and can be used under hazardous environments such as chemicals and water.